Various electromagnetic techniques exist to perform surveys of subterranean structures underneath a surface for identifying structures of interest. Examples of structures of interest in the subterranean structure include subsurface resistive bodies, such as oil-bearing reservoirs, gas injection zones, and fresh-water aquifers. One survey technique is the controlled source electromagnetic (CSEM) survey technique, in which an electromagnetic (EM) transmitter (typically towed by a sea vessel in a marine environment) is used to generate electromagnetic signals.
Surveying units (or receivers) containing electric and magnetic field sensors are deployed on the sea floor within an area of interest to make measurements (of EM wavefields) from which a geological survey of the subterranean structure underneath the surface can be derived. Through the use of the CSEM technique, a high-resolution mapping of changes in resistivity associated with the presence of oil and hydrocarbon is possible. Measurements taken by the EM receivers are interpreted in such a way that a prediction of the presence and location of oil and hydrocarbon in the sedimentary layers of the subterranean structure can be made.
One type of CSEM survey acquisition technique is a time domain (or transient) CSEM survey acquisition technique. With time domain CSEM (or TD-CSEM), a controlled EM source is turned on and then turned off after a desired waveform is transmitted (e.g., a pulse or step function, for example). A transient decay of the EM field, or an impulsive response of the EM field, as detected by EM receivers, is observed.
Inversion can be applied to the TD-CSEM data as acquired by the EM receivers to produce a model of a subterranean structure that is the subject of the CSEM survey. However, conventional inversion techniques that are applied to TD-CSEM data may not produce accurate models.